This invention is in the field of polymers used for scale inhibition in industrial water systems. Specifically this invention claims certain polymers and a method of using the polymers as a scale inhibitor in industrial water systems.
Calcium oxalate and barium sulfate scale is a persistent problem in pulp bleaching. Calcium oxalate scale is also a commonly known problem in de-inking and sugar processes and has a significant medical and biological importance.
In the pulp bleaching process, the undesirable scale generally deposits on the internal surfaces of the equipment. The scale deposits can inhibit the bleach plant process by, for example, plugging the equipment, such as, the screens, reactors, and internal passages. Chemical deposit control agents are generally known and used to alleviate the scaling problem. These agents act according to three fundamental control mechanisms, that is, inhibition, dispersion, and crystal modification.
Commercially available scale control or anti-scaling agents are typically developed to target a specific type of scale. For example, polymeric organic acids can inhibit calcium oxalate scale formation; polyacrylates can inhibit certain types of scale, not including barium sulfate; polysulfonic acids or polyphosphates can inhibit barium sulfate; and chitin and chitosan can effectively absorb metal cations.
An organic polymer based on polyepoxy succinic acid is also known to inhibit barium sulfate. However, this product is not readily biodegradable, is toxic, and is expensive to manufacture. It is also known that carbohydrates, in general, are not effective inhibitors of calcium oxalate and barium sulfate.
Accordingly, there exists a continuing need to develop an improved scale inhibiting agent, in particular an agent that targets both calcium oxalate and barium sulfate scale which are problems to industrial water systems.
The first aspect of the invention are polymers comprising:
repeating mer units of the formula: 
where X is selected from the group consisting of CO, C(H)OH, and mixtures thereof; R is selected from the group consisting of H, alkyl groups, acyl groups and mixtures thereof; and n is an integer from 1 to 400,000.
The second aspect of the invention is a method of producing a polymer, the method comprising the steps of:
providing a base polymer;
oxidizing the base polymer in a solution containing an oxidizing agent; and
recovering a polymer comprising repeating mer units of the formula: 
where X is selected from the group consisting of CO, C(H)OH, and mixtures thereof; R is selected from the group consisting of H, alkyl groups, acyl groups, and mixtures thereof; and n is an integer from 1 to 400,000.
The third aspect of the invention is method for inhibiting scale formation in an industrial water system containing an amount of scale-forming moieties, the method comprising the steps of:
providing an industrial water system;
providing a polymer comprising repeating mer units of the formula: 
where X is selected from the group consisting of CO, C(H)OH, and mixtures thereof; R is selected from the group consisting of H, alkyl groups, acyl groups and mixtures thereof; and n is an integer from 1 to 400,000;
adding an effective amount of said polymer to said industrial water system.
For purposes of this patent application the following terms have the indicated meanings:
xe2x80x9cAldrichxe2x80x9d refers to Aldrich Chemical Company, P.O. Box 2060, Milwaukee, Wis., 53201 U.S.A. telephone number (800) 558-9160, fax number (800) 962-9591.
xe2x80x9cNalcoxe2x80x9d refers to Nalco Chemical Company, One Nalco Center, Naperville, Ill. 60563, (630) 305-1000.
xe2x80x9cpolymerxe2x80x9d refers to a macromolecule formed by the chemical union of five or more identical combining units called monomers. Monomers can be abbreviated as xe2x80x9cmerxe2x80x9d or xe2x80x9cmer unitsxe2x80x9d.
The present invention provides new polymers and methods of using these new polymers for inhibiting scale, specifically, for inhibiting calcium oxalate and barium sulfate scale. The present invention includes a polymer having a number of nitrogen-containing groups and carboxyl groups. It has been found that the combined functional properties of the nitrogen-containing groups and the carboxyl groups of the present invention demonstrate desirable and advantageous scale inhibiting properties, particularly in relation to calcium oxalate and barium sulfate scale, as detailed below. Scale deposition is problematic to industrial water systems in general and in particular to industrial water systems related to the paper industry, such as, pulp bleaching, as previously discussed.
In general, the polymers of the instant claimed invention include a carbohydrate polymer having both nitrogen-containing groups and carboxyl groups, particularly from the class of carbohydrate polymers including polyaminouronic acids and polyacetamidouronic acids. This class of carbohydrates includes uronic acids having a number of nitrogen-containing groups, such as, amine groups, amide groups and mixtures thereof as described below. Uronic acids are essentially carbohydrates with carboxyl groups. In general, uronic acids are formed when a carbohydrate terminal group, such as, CH2OH, is oxidized.
In the first aspect of the instant claimed invention the polymers comprise repeating mer units of the formula: 
where X is selected from the group consisting of CO, C(H)OH, and mixtures thereof; R is selected from the group consisting of H, alkyl groups, acyl groups, and mixtures thereof, and n is an integer from 1 to 400,000.
xe2x80x9calkylxe2x80x9d refers to a fully saturated hydrocarbon moiety of from 1 to 7 carbons. The preferred alkyl moiety is methyl.
xe2x80x9cacylxe2x80x9d refers to a moiety of the formula Akxe2x80x94OCxe2x80x94, where Ak refers to an alkyl group. The preferred acyl group is H3Cxe2x80x94(O)Cxe2x80x94.
Preferably, R is H, H3Cxe2x80x94O)Cxe2x80x94, or mixtures thereof. Having this formula, the polymers of the instant claimed invention can be synthesized from natural source materials, such as, chitin and chitosan. Chitin forms the exoskeletons of living organisms, such as, insects and crustaceans. It is an inexpensive natural source that is available commercially from Aldrich. Chitin comprises repeating mer units of the formula: 
where n is an integer from 1 to 400,000.
Another source material for polymers of the instant claimed invention is chitosan. Chitosan is also available commercially from Aldrich. Chitosan may be synthesized by any suitable alkaline hydrolysis of chitin. Chitosan comprises repeating mer units of the formula: 
where n is an integer from 1 to 400,000.
The polymers of the instant claimed invention can be produced by oxidizing a base polymer. The base polymer is selected from the group consisting of chitin, chitosan, and other like material. The preferred base polymers are chitin and chitosan.
The base polymer is oxidized in a solution containing an oxidizing agent. Any suitable oxidizing agent can be used. These suitable oxidizing agents are known to people of ordinary skill in the art and can include, hypochlorite, hydrogen peroxide, ozone, N2O4, activated dimethyl sulfoxide, N-chlorosuccinimide, and other similar oxidizing agents. The preferred oxidizing agent is sodium hypochlorite.
The oxidation reaction of the present invention can also include a catalytic agent contained in the solution. The present invention is not limited to the type of catalytic agent and can include catalysts known in the art of oxidizing reactions. These catalysts, include, for example, stable radicals, particularly nitroxides such as, 2,6,6-tetramethyl-piperidine N-oxyl free radical (xe2x80x9cTEMPOxe2x80x9d), oxoammonium salts, charge transfer catalysts, such as, quaternary ammonium salts, and other like catalytic agents. The preferred catalyst is TEMPO.
It is preferred that the oxidizing reaction be conducted in the presence of a catalytic agent.
The oxidation reaction further includes maintaining a pH level ranging from about 10 to about 12. The pH level can be adjusted by utilizing any suitable acid and/or base, such as, NaOH and HCl.
The oxidation reactions of chitin and chitosan produce polymers from the class of polyacetamidouronic acids and polyaminouronic acids as previously discussed.
For example, the oxidation of chitin produces polymers from the class of polyacetamidouronic acids having repeating mer units of the formula: 
where X is selected from the group consisting of CO, C(H)OH, and mixtures thereof; and R is H3Cxe2x80x94(O)Cxe2x80x94, and n is an integer from 1 to 400,000.
The oxidation of chitosan forms polymers comprising repeating mer units of the formula: 
where X is selected from the group consisting of CO, C(H)OH, and mixtures thereof; R is H; and n is an integer from 1 to 400,000.
The oxidation of chitosan can also produce polymers containing polyacetamido groups, polyamino groups, and carboxyl groups depending on the purity of the chito san polymer. This is suggested because alkaline hydrolysis of chitin may not react to completion, thus, chitin may not completely hydrolyze into chitosan. Therefore, the chitin hydrolysized composition, i.e., chitosan, may contain both amine and amide groups. Accordingly, the oxidation of the chitosan can produce polymers that contain amine groups, amide groups, and carboxyl groups.
The present invention is not limited to polymers produced from chitin and chitosan. After oxidation of the chitin or chitosan, any suitable alkylation and/or acylation reaction can be used to provide polymers which include any suitable number and variety of acyl groups, alkyl groups, and mixtures thereof.
As previously discussed, the polymers of the instant claimed invention are desirably used to treat industrial water systems. Industrial water systems, include, but are not limited to, cooling tower water systems (including open recirculating, closed and once-through systems); petroleum wells, downhole formations, geothermal wells and other oil field applications; boilers and boiler water systems; mineral process waters including mineral washing, flotation and benefaction; paper mill digesters, washers, bleach plants and white water systems; black liquor evaporators in the pulp industry; gas scrubbers and air washers; continuous casting processes in the metallurgical industry; air conditioning and refrigeration systems; industrial and petroleum process water; indirect contact cooling and heating water, such as pasteurization water; water reclamation and purification systems; membrane filtration water systems; food processing streams (meat, vegetable, sugar beets, sugar cane, grain, poultry, fruit and soybean); and waste treatment systems as well as in clarifiers, liquid-solid applications, municipal sewage treatment and industrial or municipal water systems.
Preferably industrial water systems are those relating to the paper, food and medical industry. More preferably, the industrial water systems relate to pulp bleaching.
In the method of the instant claimed invention, the polymer compositions are added to the industrial water system in an amount of at least about 2 ppm, preferably at least about 5 ppm, and more preferably at least about 10 ppm. For purposes of this patent application, an upper limit of 1000 ppm of polymer is stated as being applicable, however, it must be understood that applying more than 1000 ppm of polymer is also going to be effective in terms of limiting scale. Therefore, the practical upper limit of the amount of polymer composition added to an industrial water system is limited only to the extent that practical considerations apply; for example, the cost associated with adding an increased amount of the polymer, the saturation point of the polymer, and other like considerations known to people of ordinary skill in the art.
The polymers of the instant claimed invention combine the functional properties of carboxyl groups and nitrogen-containing groups to effectively inhibit scale, particularly calcium oxalate and barium sulfate scale as detailed below.